# Earth's Magnetic Field

The strength and direction of Earth's magnetic field vary in space. It is described using following parameters:

## Magnetic intensity

Magnetic intensity is the magnitude of Earth's magnetic field. It is expressed in units of tesla or gauss. Its value on the earth surface is nearly 0.4 Gauss or $0.4\times10^{-4}$ Tesla.

## Magnetic declination

Magnetic declination $D$ is the angle between true north and magnetic north, and varies depending on the observer's location on the Earth's surface. It's value is approximately 11.5 degree.

## Magnetic inclination (or angle of dip)

Magnetic inclination or angle of dip $\delta$ is the angle between the direction of the magnetic field lines and the horizontal plane at a given location.

## Problems from IIT JEE

Problem (JEE Mains 2022): The vertical component of the earth's magnetic field is $6\times{10}^{-5}$ T at any place where the angle of dip is $37^\circ$. The earth's resultant magnetic field at that place will be (Given $\tan37^\circ=3/4$)

1. $8\times10^{-5}$ T
2. $6\times10^{-5}$ T
3. $5\times10^{-4}$ T
4. $1\times10^{-4}$ T

Problem (JEE Mains 2022): At a certain place the angle of dip is 30 deg and the horizontal component of earth's magnetic field is 0.5 G. The earth's total magnetic field (in G), at that certain place, is

1. $\frac{1}{\sqrt{3}}$
2. $\frac{1}{2}$
3. $\sqrt{3}$
4. 1

or